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Abstract

Four very low birth weight, very premature infants were monitored during a 12° postural elevation using diffuse correlation spectroscopy (DCS) to measure microvascular cerebral blood flow (CBF) and transcranial Doppler ultrasound (TCD) to measure macrovascular blood flow velocity in the middle cerebral artery. DCS data correlated significantly with peak systolic, end diastolic, and mean velocities measured by TCD (pA=0.036, 0.036, 0.047). Moreover, population averaged TCD and DCS data yielded no significant hemodynamic response to this postural change (p>0.05). We thus demonstrate feasibility of DCS in this population, we show correlation between absolute measures of blood flow from DCS and blood flow velocity from TCD, and we do not detect significant changes in CBF associated with a small postural change (12°) in these patients.

Diagram of the protocol used for DCS (top) and TCD (bottom) measurements. DCS and TCD measurements were NOT taken at the same time. For DCS, data was taken continuously (8 data points per minute) for 5 minutes at each head of bed angle adjustment. The head of bed 0° to 12° elevation was repeated 3 times, making the total study time 35 minutes. By comparison, for TCD only 3 data points were taken at each HOB angle before the bed was repositioned, and the HOB angle was only elevated twice.

(Left) Typical normalized intensity autocorrelation curve derived directly from the correlator board as a function of time, τ (data measured on the forehead of a preterm infant). (Right) The corresponding normalized electric field autocorrelation curve, g1(r,τ), calculated using the Siegert relation with a fitted value for β. The solid line shows the raw data. The dotted line is the best fit curve to a Brownian motion model, which we use to derive the blood flow index (BFI).

(Left) Correlation between population averaged mean TCD PSV taken at the initial (PSV¯) and population averaged mean DCS BFI also taken at the initial (BFI¯). (Center) Correlation between population averaged mean TCD MV taken at the initial (MV¯) and DCS BFI¯. (Right) Correlation between population averaged mean TCD EDV taken at first HOB=0° event (EDV¯) and DCS BFI¯. The solid line in each plot shows the best linear fit between the two variables. Both Pearson’s and Spearman’s correlation coefficients (R2 and rs, respectively) were calculated. The R2 Pearson values are displayed for each plot.